When an aircraft model is tested in a wind tunnel, test data is often sought on the forces (normal side, and axial) and moments (yaw, pitch, and roll) exerted on the model. An apparatus for measuring these forces and moments is called a balance. Prior to usage in a wind tunnel, the balance must be calibrated. One commercial device made for calibrating balances applies adjustable calibration forces to the outer body of the balance and repositions the balance back to a central reference point to compensate for changes in alignment due to the applied forces. The user of the calibration device must position and measure the calibration forces. In order to achieve a total error of 0.1% or less, the applied forces need to be accurately known to about 0.03%, and the position and direction that the forces are applied must be known to approximately 0.001" and 0.002 degrees, respectively. To assure that the normal, side and axial calibration forces are pure and do not interact with each other or produce erroneous moments, the normal, side and axial forces must pass through the central reference point and be mutually perpendicular.
Reticles which include cross hairs are widely used for optical alignment. The following U.S. patents, for example, disclose cross hair reticles: 730,016, Hein; 1,189,422, Bodmer; 2,466,724, Meyer; and 4,380,876, Strassburg. These reticles are intended for single, not multiple axis optical alignment. The principal object of this invention is to provide a reticle which uses a minimum number of filments or cross hairs and permits the precise alignment of up to three orthogonal axes that cross at a common target point.